In the related art, there have been known fluorescence observation apparatuses that acquire a reference image, such as a white-light image, capturing the morphology of a subject, and a fluorescence image visualizing a lesion by capturing fluorescence from the subject, and that display the lesion within the fluorescence image with the lesion superimposed on the reference image (for example, see Patent Literatures 1 and 2).
In Patent Literature 1, the fluorescence image is added to any of a red-component image, a green-component image, and a blue-component image constituting the color reference image to thereby display the lesion as a red, green, or blue region on the reference image. In this case, since the reference image includes information on original gradation values, i.e. information on the morphology of the subject, in a region displaying the lesion, the morphology of the lesion can also be observed. In Patent Literature 2, the region of the lesion in the reference image is filled with a false color. In this case, the visibility of the lesion will be improved.